# For our example dataframe
import pandas as pd
# For our plot
import matplotlib.pyplot as plt

# Generating sample data
df = pd.DataFrame({"col1": range(10)})

# Creating a figure and the axes for our plots
fig, axes = plt.subplots(1,1, figsize=(8,6)) 

# We plot a hline
axes.hlines(y=2,
            xmin=0,
            xmax=df["col1"].max())

# We make our canvas tidy and clean
plt.tight_layout()

# We show the graph
plt.show()